The need to hold one thing relative to another thing is ubiquitous in industry. For example, it is generally very difficult or impossible to perform accurate and precise actions on or with respect to a workpiece if the workpiece cannot be held securely and accurately. Robotics rely extensively on the ability to hold a tool or other process implement relative to the workpiece, hold the workpiece relative to the implement, or both. The demand for holding devices is particularly acute in precision systems.
An example precision system that imposes extremely demanding performance from all its constituent components and assemblies is a microlithography system. Whereas until recently microlithography was directed principally to the manufacture of microcircuits and related devices, it is also an important tool for the manufacture of large panel displays such as liquid crystal displays. So as to be imprinted with a desired pattern of display elements (pixels), a substrate panel is supported on a large platen called a plate holder (PH). The PH is supported by a plate table (PT). The PT functions as a movable stage that can be displaced to any of various positions as the patterns are imprinted on the surface of the substrate panel. The PH functions as a large chuck that holds the substrate panel. The PT and PH can be very large and massive. The PH desirably is supported so that the surface thereof on which the substrate is placed remains substantially planar, without significant sag or other surface deformation resulting from unsupported or improperly supported mass.
Currently, the PH is supported on the PT using bolts placed between the PH and PT at predetermined locations. For adjustability of the flatness of the PH, shims are conventionally inserted between the PT and PH. This adjustment is performed at time of manufacture, at the time of installation, and at other times as required. Unfortunately, this manner of attachment requires substantial manual labor and is difficult and time-consuming to perform. Also, in view of the fact that the PH and PT are normally fabricated of different materials, this mounting and adjustment scheme also does not allow for relief of thermal stresses that otherwise could accumulate in the PH and cause warping or other deformation thereof. Whereas bolts are typically very stiff in the vertical direction, the connections made at the contacts by the bolts are also very stiff in both horizontal directions, particularly when the bolts are tightened. These very high stiffness values do not allow, for example, significant relaxation of a PH experiencing thermal expansion. Finally, whereas use of bolts and shims in this manner can provide stability of the PH, relative to the PT, down to the micrometer range, they are very difficult to adjust.
Therefore, conventional devices and methods for holding a first mass (e.g., a PH or analogous component) relative to a second mass (e.g., a PT or analogous component) do not address the need to provide a combination of stiffness in the vertical direction and in one horizontal direction, flexibility in the other horizontal direction, strength and stability under load, ease of adjustability, accuracy of adjustability in height and angle of the object being held, and capability of being used in conjunction with a mover or actuator operable to change position of the object being held in 3-D space.